Electric blasting cap



March 29, 1949. J. B. MORTON 2,455,467

' ELECTRIC BLASTING CAP Filed June 11, 1946 FIG! FIG-2 JOHN B. MORTONINVENTOR.

Patented Mar. 29, 1949 UNITE.

ELECTRIC BLASTING CAP John B. Morton, Hopewell, Va., assignor toHercules Powder Company, Wilmington, DeL, a

corporation of Delaware Claims.

This invention relates to an improved electric blasting cap and, moreparticularly, to a safetytype electric blasting cap.

It is well known that an electric blasting cap of the safety type mayhave a base charge comprising a secondary explosive and a priming chargesuperimposed thereon comprising an explosive of the so-called safetytype, such as the nitrated saccharides, nitromannite and nitrolactose.These priming charges are ignited by means of a deflagratablecomposition or by means of a semi-explosive burst from a matchhead-typeassembly superimposed thereon. These caps are known to be less sensitivetoward detonation upon the application of strong external heat thansimilar blasting caps having a primary charge comprising such explosivesas mercury fulminate, diazodinitrophenol, lead azide, etc. Safety-typeelectric blasting caps have several disadvantages, one being that theignition charge necessary to set off the safety-type primary charge musthave unusually strong ignition characteristics, another being that thepriming charge requires an added confinement comprising a reinforcingcapsule or inner shell in order to be fully effective, and still anotheris that, in most instances, relatively greater amounts of the safetytypepriming charge must be used in order to efiect proper detonation of thebase charge.

Now in accordance with the present invention it has been discovered thatwhen a high heatstable primary charge of lead azide is positionedcentrally and in the upper portion of a heatunstable priming orexplosive charge, such as nitrolactose which is in turn superimposedupon a base charge, the disadvantages found with prior art safety-typeelectric blasting caps are eliminated.

It is an object of this invention to provide an electric blasting capwhich may be heated externally to a high temperature without causingdetonation.

Another object of this invention is to provide a safety-type electricblasting cap that is simple in construction, economical to manufactureand reliable.

Other objects of the invention will appear hereinafter, the novelfeatures and combinations being set forth in the appended claims.

Preferred embodiments of this invention have been chosen for the purposeof illustration and description and are shown in the accompanyingdrawing, forming a part of the specification wherein:

Fig. 1 is an elevational view in partial section of the electricblasting cap in the course of construction; and

Fig. 2 is an elevational view in partial section of the completed cap.

An improved electric blasting cap was manufactured in accordance withthe present invention by placing a base charge 1 comprising 0.20 gram oftetryl into a shell 2 of 0.30-inch inside diameter, and pressed with aflat pin under a pressure of 4000 pounds per square inch. Aheat-unstable priming charge 3, consisting of 0.12 gram of nitrolactose,was superimposed on top of the tetryl base charge and pressed with astep-cut pin 4 under a pressure of 200 pounds per square inch. The useof the step-cut pin, shown in Fig. 1 being withdrawn from the shell 2,forms a cavity 5 centrally located in the priming charge 3 and locatedin the upper portion thereof. The dimensions of the cavity 5 may bechanged in such a way as to vary the depth to which the cavity extendsinto the priming charge 3, depending upon the length of the column ofpriming charge being used. The cavity is positioned as near the centerof the priming charge as is possible so as to provide the maximum amountof insulation and cushioning by that portion of the priming charge 3indicated by the numerals 6 for a given amount of heat-stable primarycharge.

A heat-stable primary charge 1 comprising 0.02 gram of lead azide ischarged into the minimum volume cavity 5 after which the ignition chargeand the priming charge are pressed simultaneously with a flat pin undera pressure of 2000 pounds per square inch. A bridge assembly, comprisinga plug 8 having a cavity 9 at the lower end thereof and a pair of spacedleg wires I0 extending therethrough and terminating adjacent the cavity9 in a pair of bridge wire supports connected by a bridge wire H, ismoved into the open end of the shell 2. The cavity 9 was previouslyfilled with an ignition charge l2 consisting of 19.0%diazodinitrophenol, 65.8% potassium chlorate, 13.2% charcoal, and 2.0%nitrostarch. Thus, the ignition charge is placed in juxtaposition to theprimary charge as shown in Fig. 2. The shell was then closed againstmois ture with a waterproofing compound 13 and a sealing compound M.

Electric blasting caps prepared in accordance with the above examplegive an excellent lead plate test in accordance with the standards setup by the U. S. Bureau of Mines.

Electric blasting caps prepared in accordance with the above examplewere tested to determine their sensitivity to ignition from extreme heatby placing the caps in a molten metal bath at various temperatures. Theresults of these tests are given in the table, column 1.

More electric blasting caps were made similar to the above example,except that the heat-stable primary charge, lead azide, was positionedin a layer over the entire top surface of the priming charge whichconsisted of 0.22 gram of nitrolactose. Ihese caps were also subjectedto the same molten metal bath test and the results are given in column 2of the table. Five caps of each type were tested at the temperaturegiven in the table.

Temperature I Tune for Dsecomposition, AV

Sec.

' Time for Decomposition.

- Ulla momma-cc: town-named:

Total partia 2; column two, .5.

1 Partial shots.

2 Cap detonated completely.

shots, column '1, 2; column two, 6.

It is noted that the tendency toward detonation with increased externalheat is less pronounced with caps in which the lead azide is centrallypositioned on the top side of the priming charge than with caps in whichthe lead azide is positioned over the entire top surface of the primingcharge. The charges in which the lead .azide was centrally positionedwere decomposed. at a slower rate than those in which the lead azide wasposi tioned over the entire top of the surface.

Tests of these two types of caps for purposes of determining the minimumpriming charge necessary to detonate a base charge of tetryl indicatethat, for a given amount of a priming charge of nitrolactose, a lesserWeight of primary charge of lead azide is necesary when the lead azideis carried in a minimum volume cavity positioned centrally and on thetop side of the priming charge than when the lead azide is spread in theform of a wafer over the entire top side surface of the priming charge.

Suitable safety-type priming charges operable in accordance with thisinvention are solid nitrated saccharides, such as, for example,nitrolactose, nitromannite, nitrosucrose, nitroinositol, etc.

Suitable base charges are any of the base charges commonly used inelectric blasting caps such as, for example, tetryl, trinitrotoluene,nitrost'arch, PETN, etc. The preferred combina tion of charges is acombination of charges wherein the base charge is tetryl, the primingcharge is nitrolactose, and the primary charge is lead azide.

In U. S. Patent 1,928,207 to Large, it is shown that 0.05 gram ofnitrolactose is necessary to detonate a tetryl base charge The capsprepared in accordance with this invention use 42% less nitrolactosewhen combined with lead aside in the manner disclosed to effect the samedesirable detonation of the base charge of tetryl. In accordance withthis invention, the minimum priming charge necessary to detonate thetetryl will vary in accordance with the proportional Total completeshots, column one,

In all other cases, cans miffed without vio ence,

electric blasting caps where primary charges of lead azide,diazodinitrophenol, mercury fulminate, etc., are used. Inccntradistinction to the strong ignition charges necessary in order toproperly ignite a safety-type electric blasting cap, the presentinvention provides for the use of the conventional and well-known typesof ignition compositions in juxtaposition to the primary charge.

From the foregoing description, it is apparent that the objects of thisinvention have been accomplished by providing a safety-type electricblasting cap comprising a primary charge of lead azide positioned inminimum volume cavity held in insulated and cushioned relationship withthe shell of the detonator on the top side .of a heatunstable priming chrge, whereby a minimum amount of priming charge is necessary in order toproperly detonate the base charge.

What I claim and desire to protect by Letters Patent is:

1. An electric blasting cap having in combination a base charge, aheat-unstable priming charge superimposed on the base charge, a primarycharge of lead azide disposed centrally in the upper portion of thepriming charge, and an ignition charge in juxtaposition to the primarycharge.

2. An electric blasting cap having in combination a base charge, apriming charge or a solid nitrated saocharide superimposed on the basecharge, a primary charge of lead azide disposed centrally in the upperportion of the priming charge, and an ignition charge in juxtapositionto the primary charge.

3. An electric blasting cap having in combination a base charge, apriming charge of nitrolacetose superimposed on the base charge, aprimary charge of lead azide disposed centrally in the upper portion ofthe priming charge, and an ignition charge in juxtaposition to theprimar charge.

An electric blasting cap having in combination a base charge, a primingcharge of ni- 5 tromannite superimposed on the base charge, a primarycharge of lead azide disposed centrally in the upper portion of thepriming charge, and an ignition charge in juxtaposition to the primarycharge.

5. An electric blasting cap having in combination a base charge, apriming charge of nitrosucrose superimposed on the base charge, aprimary charge of lead azide disposed centrally in the upper portion ofthe priming charge, and an ignition charge in juxtaposition to theprimary charge.

6. An electric blasting cap having in combination a heat-unstableexplosive charge, a charge of lead azide disposed centrally in the upperportion of the heat-unstable explosive charge, and an ignition charge injuxtaposition to the charge of lead azide.

7. An electric blasting cap having in combination a heat-unstableexplosive charge of a solid nitrated saccharide, a charge of lead azidedisposed centrally in the upper portion of the heatunstable explosivecharge, and an ignition charge in juxtaposition to the charge of leadazide.

8. An electric blasting cap having in combination a heat-unstableexplosive charge of nitrolactose, a charge of lead azide disposed cen-6? trally in the upper portion of the heat-unstable explosive charge,and an ignition charge in juxtaposition to the charge of lead azide.

9. An electric blasting cap having in combination a heat-unstableexplosive charge of nitromannite, a charge of lead azide disposedcentrally in the upper portion of the heat unstable explosive charge,and an ignition charge in juxtaposition to the charge of lead azide.

10. An electric blasting cap having in combination a heat-unstableexplosive charge of nitrosucrose, a charge of lead azide disposedcentrally in the upper portion of the heat-unstable explosive charge,and an ignition charge in juxtaposition to the charge of lead azide.

JOHN B. MORTON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,928,208 Large Sept. 26, 19332,086,532 Burrows July 13, 1937 2,350,172 Lawrence May 30, 19442,402,235 Burrows June 18, 1946 Certificate of Correction Patent No.2,465,467. March 29, 1949.

JOHN B. MORTON It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 3, line 67, for 0.05 gram read 0.50 gram; column 4, lines 68 and69, for nitrolacetose read nitrolactose; and that the said LettersPatent should be read with these corrections therein that the same mayconform to the record of the case in the Patent Ofilce.

Signed and sealed this 30th day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,465,467. March 29, 1949.

JOHN B. MORTON It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 3, line 67, for 0.05 gram read 0.50 gram; column 4, lines 68 and69, for nitrolacetose read nitrolactose;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Ofiice.

Signed and sealed this 30th day of August, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

